Finished wrapping up the harness this afternoon. Just a couple of pieces to finish, but I'll leave those until it's in the truck and I know exactly where everything needs to be.

I also made a start on tearing down the motor. It's certainly been stood outside uncovered at some point. Haven't got as far as pulling the oil pan yet, but hopefully will do that tomorrow and see if there's any damage. Hopefully there won't be! Looks ok so far with the exception of some very minor pitting in one bore, which I hope will hone out.

Tearing it down does at least mean I get to be 100% happy that everything is good and there won't be any surprises down the line

The LS to GMT400 harness is pretty simple from what I can make out. Aside from the power and ground connections:

1.The oil pressure sensor isn't used by the LS PCM, so replace the LS sensor with the one from the original engine to make the gauge work. I left the cable in my harness and will just change the connector on the end to suit the old engine sensor
2. The water temperature sensor - you need to use both the original and the LS one. The LS one goes to the PCM and the original is screwed into an adapter in the other head to make the gauge work.
3. The RPM counter takes the tach signal from the PCM
4. The speedo takes the speed signal from the PCM - might also be needed for the cruise system? Not sure yet.
5. If 4wd, then use the sensor on the transfer case and splice into the speed sensor wires in the LS harness.
6. The back up light power comes from the range switch on the transmission, so that will need to be splice in too.

Aside from that, I can't think of much else. You might want to use things like the AC or whatever, but just figure them out as you go.

The LS to GMT400 harness is pretty simple from what I can make out. Aside from the power and ground connections:

1.The oil pressure sensor isn't used by the LS PCM, so replace the LS sensor with the one from the original engine to make the gauge work. I left the cable in my harness and will just change the connector on the end to suit the old engine sensor Correct, the LS PCM does not need the oil pressure sensor. My question was, how are you going to connect the old engine sensor to the LS block? I was thinking the old unit would have to be rethreaded to metric.
2. The water temperature sensor - you need to use both the original and the LS one. The LS one goes to the PCM and the original is screwed into an adapter in the other head to make the gauge work.Correct
3. The RPM counter takes the tach signal from the PCMCorrect, I assume that is Red pin 10 (for the 99-02 harness, lt1swap.com) Where is the tach wire from the instrument cluster?
4. The speedo takes the speed signal from the PCM - might also be needed for the cruise system? Not sure yet.Does the speedo take the speed signal from the C100's VSS that you spliced the LS VSS into or is it the Red/Green pin 50?
5. If 4wd, then use the sensor on the transfer case and splice into the speed sensor wires in the LS harness.See above, this is where its getting confusing for me.
6. The back up light power comes from the range switch on the transmission, so that will need to be splice in too.This is where our swaps differ. Since I am using a manual tranny, I just needed to snip a few wires from the tranny harness and buy a new connector for the manual, splice those two together and I have backup lights.

Aside from that, I can't think of much else. You might want to use things like the AC or whatever, but just figure them out as you go.A/C is another issue I'm tackling at the moment. I haven't quite gotten those figured out either.

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These are the wires I have loose at the C100:

C100 A2 PNK Connect to where?
C100 B6 BRN/WHT I connected this to Red pin 46 - Malfunction Indicator Lamp. I believe it is correct.
C100 C2 YLW This is one of those safety switches, Im just not sure where it connects too. Ive been away from the project for a while, but I do believe this is part of the starter circuit.
C100 C3 BRN Splice into R15 BRN? - I believe this is the volt signal for the cluster. This is just a guess though.
C100 C5 GRN Connect to where? This is the coolant temperature indicator lamp output.
C100 D2 LTBLU/BLK CC Engine Signal. From what Ive read, this tells the cruise control to shut off because the clutch is being pressed.

I stripped the rest of the motor down tonight, just the crank and cam to remove now, but the hardest part is done. Getting the crank pulley off. The bolt is done up FT... and the pulley is a press fit on the crank snout at well. Hard to get a puller on it unless you have the special tools, which are hard to find in the UK.

But a lump of wood to jam the crank while cracking the bolt free and a lightly modified puller made getting it off reasonably easy....

I'll get the crank and cam out over the weekend and the block cleaned, measured and checked before honing the cylinders and getting it ready for rebuild.

Plus it's been raining hard all day today so I decided to get the transmission rebuilt. I needed to strip it down to fit the 4wd output shaft anyway. Pulled the pan off and found it was full of clutch material. Turned out there were 2 toasted clutch packs and one check ball wedged firmly in the separator plate. I expect that was a contributing factor.... Aside from that I couldn't find any major issues with it other than the normal wear you would expect.

HEG frictions throughout including 3-4 powerpack (1 extra steel and friction), alto red eagle band, corvette servo, Transgo HD2 shift kit then new seals and stuff throughout. Should all help it live for a long time in my truck as it will mainly be towing